Legionnaires' disease is a type of pneumonia that normally affects people over 50, or people who have compromised immune systems or chronic lung disease, according to the CDC. Current and former smokers are also at a greater risk to contract the disease.

The most common form of exposure is to people who breath in a mist or vapor containing the bacteria.

There are an estimated 8,000 to 18,000 cases of Legionnaires' disease in the U.S. each year.